Rabbit FM01 and FM02 and human FM03 cDNAs will be expressed in AHH-1TK+/- human lymphoblastoid cells, AS52 Chinese hamster cells and C3H 10T1/2 mouse cells. FMO expression will be monitored by regio- and stereoselective/enzyme assays and immunoblotting. The level and stability of FMO expression will be monitored in the cDNA expressing cell lines. The differences in xenobiotic metabolism by allelic variants of human FM03 will be examined. The FMO-expressing human lymphoblastoid cell lines will compliment an existing panel of cell lines expressing cytochrome P450 enzymes. AS52 cells will allow the facile analysis of mutational spectrum for promutagens activated by FMO. The C3H 10T1/2 cell lines will allow extension of in vitro toxicology studies to the malignant transformation endpoint. PROPOSED COMMERCIAL APPLICATION: Mammalian cells expressing flavin- containing monoxygenases will have commercial applications for the in vitro analysis of xenobiotic metabolism and toxicity. This new system complements an existing system containing cytochrome P450 enzymes.